Aluminum base alloys



2,993,783 ALUMINUM BASE ALLOYS Wayne Martin, 19820 Battersea Blvd, RockyRiver, OhlO,

assignor to William F. Jobbins, Incorporated, Aurora,

111., a corporation of Illinois No Drawing. Filed July '21, 1960, Ser.No. 44,252 12 Claims. (Cl. 75-146) This invention relates to an aluminumbase alloy of the type referred to in the trade as a sand cast alloy,and it relates more particularly to a sand cast alloy which isself-aging to enable the development of high strength in as castcondition and which develops outstanding properties in response tosolution heat treatment and artificial aging.

It is an object of this invention to produce an aluminum base alloy forsand casting which may be used without heat treatment in applicationsrequiring high strength but which also may be subjected to heattreatment for the further development of properties heretoforeunavailable for aluminum base casting alloys.

Another object of this invention is to produce a sand cast aluminum basealloy of high strength in as cast condition and which is capable ofself-aging in as cast condition for the development of strengthproperties heretofore unavailable Without heat treatment.

In accordance with the practice of this invention, the aluminum basecasting alloy is formulated to contain aluminum as the base materialwith Zinc, magnesium, chromium and titanium as essential alloyingelements, and boron and zirconium as additional alloying elements whichcan beneficially be included in the alloy. It has been found that thedevelopment of the properties desired in the casting alloy dependsgreatly upon the formulation of the alloy with less than 0.75% by weightof element other than the described base metal and the foregoingalloying elements, with no one component of the residual metals orimpurities making up said other elements being present in an amountgreater than 0.25% by weight.

It has been found further, and it is an important concept of thisinvention, that the alloying elements be present in the composition inamounts which are critical to the development of the desiredcharacteristics in the alloy, and that substantial deviation from thefairly narrow range of each of the alloying elements in the compositionwill be reflected by noticeable change in the physical and mechanicalproperties that are secured in the alloy. It is believed that theimportance of each of the essential alloying elements and the amountsthereof in the base alloy can best be demonstrated by a series ofevaluations of alloys wherein the amounts of the alloying elements havebeen varied.

For demonstration as to the importance of zinc and the amount thereof inthe aluminum base alloy, a series of melts were prepared embodying thebasic features of this invention but in which variation Was made only inthe amount of zinc in the alloy. The basic composition of the alloy,other than the zinc component, was as follows:

EXAMPLE 1' a Percent by wgt. Magnesium I 0.75 Chromium 0. Titanium 0.20Boron 0.001 Iron 0.05 Silicon 0.07 Tin 0001 Lead 0.001 Copper 0.25Manganese 1 Max.

Patented July 25, 1961 The amount of zinc in the base alloy was variedfrom 5 to 10% by weight in increments of a whole percent. Test bars weresand cast of the alloy and were subjected to solution heat treatment for12 hours at 960 F., fol lowed by quenching in water maintained at atemperature of about 180 F. The quenched bars were artificially aged byheating for 5 hours at a temperature of 250 F. The results are set forthin the following Table I:

From the results secured, it will be apparent that the strength risessharply when zinc is present in an amount greater than 5%. While thestrength properties continue to increase with increased amounts of zinc,it

will be apparent that elongation falls suddenly to unacceptable levelswhen the amount of zinc is increased to as much as 9%. Best results aresecured when the amount of zinc is limited to within the range of5.5-8.5 and preferably to within the range of 68%. It has been foundthat the amount of zinc within the range described above is applicableto all of the alloy systems within the confines of this invention.

In a similar manner, the amount of magnesium has been determined byvariation of the amount of magnee sium in an alloy system embodying thefeatures of this invention. For this purpose, use was made of an alloyhaving the following basic composition other than magnesium:

In this examination, the amount of magnesium was varied from 0.5 to 1.0%in increments of 0.1%.

Test bars sand cast of the alloy systems were solution heat treated for12 hours at 960 F followed by quench ing in water maintained at about180 F. The quenched bars were artificially aged by heating for 5 hoursat a tem perature of about 250 F. The results are set forth in thefollowing Table II:

Table 11 Amount; of Mag- Ult. Strength Yld. Strength Elongation innesrum 111 p.s.i. in p.s.i. percent From the results secured, it will beapparent that the strength rises quite rapidly when the amount ofmagnesium exceeds 0.5% until the amount of magnesium reached 0.9%.Thereafter, no substantial increase in strength properties is secured byfurther increase in the amount of magnesium. The upper limitation in theamount of magnesium is defined by the marked reduction which isexperienced in the elongation when the amount of magnesium exceeds 0.9%.Thus, in the practice of this invention, it is important to maintain theamount of magnesium in the sand cast alloy within the broad range of0.550.95%, and preferably to Within the range of 06-08%.

Similar investigations have established that limitations also exist withrespect to others of the alloying elements present in the aluminum basealloy of this invention. The amount of chromium should be limited towithin the range of 0.0250.25% by Weight of the alloy, and preferably toWithin the range of 0.05-0.15% by weight.

- The amount of titanium should be in excess of 0.05% by weight. Whilemore than 0.4% by Weight titanium can be used, no correspondingimprovements are secured by reason of such additional amounts oftitanium. It is preferred to limit the amount of titanium to within therange of 0.100.25% by weight of the alloy composition.

When boron is present in the alloy, the amount of boron should be lessthan 0.002%, but best practice limits the amount of boron to within therange of 0.0005- 0.001% by weight. Zirconium, when present, should belimited to an amount less than 0.35% by weight, and preferably to anamount within the range of 0.05-0.25% by weight.

Iron and silicon represent residual metals which have been found to havea most undesirable effect upon the properties of the alloy when eitheris present in an amount greater than 0.15% by weight. This can beillustrated by the examples which will hereinafter be set forth. In analloy of Examples 1 and 2, wherein the magnesium is present in theoptimum amount of 0.75% and the zinc is present in the optimum amount of7%, test bars were cast from melts in which, in one instance, the ironcontent was varied horn 0.12% to 0.25% by weight and, in anotherinstance, the silicon was varied from 0.10% to 0.25% by weight. The casttest bars were evaluated in as cast condition and after the test barswere subjected to solution heat treatment and artificial aging. Thefollowing tables set forth the values that were secured:

Table III COMPARISON OF STEEL BARS IN AS CAST CONDITION IN WHICH IRONCONTENT IS VARIED COMPARISON OF STEEL BARS OF TABLE III AFTER SOLU- TIONHEAT TREATMENT Amount of Iron Ult. Strength Yld. Strength Elongation inin p.s.i. in p.s.i. percent 4 Table V COMPARISON OF STEEL BARS IN ASCAST CONDITION VARIATION IN SILICON Amount of Silicon Ult. Strength Yld.Strength Elongation in in p.s.i. in p.s.i. percent Table VI COMPARISONOF STEEL BARS OF TABLE V AFTER SOLU- TION HEAT TREATMENT Amount ofSilicon Ult. Strength Yld. Strength Elongation in v in p.s.i. in p.s.i.percent While no material differences were observed in the strengthproperties or elongation in as cast condition tor variation in theamount of iron, the elongation falls off undesirably when the ironcontent is as high as 0.16% after the bars have been subjected tosolution heat treatment and artificial aging. Thus the amount of ironshould be held to less than 0.16% and it is believed that the upperlimitation can properly be placed at 0.15 by weight of iron.

With respect to silicon, the strength properties of the as cast alloyfalls off materially when the amount of silicon exceeds 0.15% by weight.A similar drop in strength is experienced also in the alloy subjected tosolution heat treatment, but the values secured are so unexpectedly highin the first instance that the drop in strength is still acceptable.

The foregoing Tables HI-VI will also illustrate the exceptionally highstrength properties that are secured with the alloy of this inventionupon solution heat treatment and artificial aging. One of theoutstanding characteristics of the alloys embodying the features of thisinvention is the ability of the alloy to self age the as cast conditionto provide strength properties which have not heretofore beenavailablein sand cast alloys. This makes available an alloy which can beput to a number of uses that were not heretofore open to aluminum or itsalloys. The alloys having these unexpected self-aging properties andhigh strength in as cast condition are also subject to solution heattreatment to provide alloys of exceptionally high strengths, aspreviously pointed out. The foregoing can be illustrated by thefollowing examples.

two weeks, it increased to 43,010. After three weeks, it increased to43,320, and after three months the ultimate strength reached a value of44,000 or slightly better. The yield strengths were similarly increasedfrom 21,980 as cast, to 28,920 after one week, to 31,880 after twoweeks,

5 to 33,170 after three weeks, and to better than 36,000 after threemonths aging. The elongation varied from 10.8% as cast to 5.5% afterthree weeks, and a minimum of 5% after three months aging.

Aluminumremainder (with less than 0.75%

residual metals and impurities). 1 Max.

The following are the results secured of the alloy of 6 EXAMPLE 7 Alloycomposition:

Elements- Percent by wgt. Zinc 6-8 Magnesium 0.6-0.8 Chromium ODS-0.15Titanium 0.10-0.25

Aluminumremainder (with less than 0.75%

residual metals and impurities).

EXAMPLE 8 Percent by Wgt. Alloy Composition-Elements Broad Range NarrowRange 1 Remainder (with less than 0.75% residual metals and impurities).

EXAMPLE 9 Example 4 after aging for one day, one week, one month,

I 25 and three months An 0 t. E] t Percent by g 0y omposl 1011'- emell 5Time of Aging U.S., p.s.i. Y.S., p.s.i. 15215; Hagginlerss, Broad RangeNarrow Range 1 d 38,000 25, 000 11 70 lw kfl 39, 000 27, 000 s 80 gg iggg 218-5 1 000 000 5 Tit a il i il 005-0140 0: 10-0 25 3 000 000 4 91Boron -IIII 0. 0002-0. 001 0. 0005-0. 001

Zirm Less than 0.35 0. 05-0. 25 EXAMPLE 5 Aluminum 0) (1) Alloycomposition: 35 1 Remainder (with less than 0.75% residual metals andimpurities).

E1emePtS Percent by When the total impurities and residual metals,includ- Zmc 6.5 ing the iron, silicon, copper, manganese and sodium, ex-Magnes lum 9' ceeds 0.75% by weight of the alloys, an undesirable drop hf 0'05 0'15 40 in the physical and mechanical properties is experiencedTlta'mum (Ho-0'25 both in the as cast and in the heat treated condition.Boron Thus it is undesirable to permit the silicon and iron to 2 1exceed 0.15% each or to permit the amount of copper 1 to exceed 0.25% orto permit the amount of manganese Tm 1 0901 to exceed 0.10%, or topermit the silicon, iron, copper, Lead 10001 tin, sodium and lead toexceed a total of'0.75%. The Copper 1 025 amount of such other residualmetals should not exceed Manganese the maximum set forth in Examples 4and 5.

Aluminum-remainder (with less than 0.75%

residual metals and impurities).

Max.

The following are the results which are secured after self aging for oneday, one week, two weeks, three weeks, and four weeks:

Time of Aging U.S., p.s.i. Y.S., p.s.i. Elong, Hardness,

Percent BEN 86, 000 20, 000 14 55 37, 000 24, 000 12 65 38,000 27,000 1070 39, 000 30, 000 9 80 4 weeks 40, 000 32, 000 8 85 The following arefurther illustrations of formulations of aluminum base alloys embodyingthe features of this invention:

Aluminumremainder (with less than 0.75%

residual metals and impurities).

It will be apparent from the foregoing that I have provided an aluminumbase alloy capable of self aging to produce what is believed to befantastically high yield strengths in the as cast condition. A value inthe order of 44,000 p.s.i. for ultimate strength in as cast aluminumalloy has, to my knowledge, never previously been available. Similarly,ultimate strengths in the order of 50,000 p.s.i. and yield strengths of42,000 p.s.i., with elongations as high as 6-8% as secured by heattreatment of the alloys of this invention, are also believed to beunexpectedly secured with an aluminum base alloy.

It will be understood that changes may be made in the details offormulation and preparation without departing from the spirit of theinvention, especially as defined in the following claims.

I claim:

1. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 6-8% by weight, magnesiumpresent in an amount Within the range of 06-08% by weight, chromiumpresent in an amount within the range of 0.05- 0.15 by weight, andtitanium present in an amount within the range of 0.1-0.25-% by weight,the remainder being aluminum plus minor amounts of impurities.

2. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 6-8% by weight, magnesiumpresent in an amount within the range of 06-08% by weight, chromiumpresent in an amount within the range of 0.05-0.15% by weight, titaniumpresent in an amount within the range of 0.10.25% by weight, and lessthan 0.75% by weight of impurities, the balance being aluminum.

3. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 6-8% by weight, magnesiumpresent in an amount within the range of 06-08% by weight, chromium present in an amount within the range of 0.050.15% by weight, and titaniumpresent in an amount Within the range of OJ-0.25% by weight, and lessthan 0.75% by weight of impurities including a maximum of 0.15% byweight of any of the metals selected from the group consisting ofsilicon and iron, the balance being aluminum.

4. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 68% by weight, magnesiumpresent in an amount within the range of 06-08% by weight, chromiumpresent in an amount within the range of 0.05- 0.15 by weight, titaniumpresent in an amount Within the range of 0.10.25% by weight, and boronpresent in an amount within the range of 0.00=0.00l% by weight, theremainder being aluminum plus minor amounts of impurities.

5. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 6-8% by weight, magnesiumpresent in an amount within the range of 0.60.8% by weight, chromiumpresent in an amount within the range of 0.050.15% by weight, titaniumpresent in an amount within the range of 01-025 by weight, and boronpresent in an amount within the range of 0.00050.001% by weight, andless than 0.75% by weight of impurities, the balance being aluminum.

6. A self-aging aluminum base casting alloy consisting essentially ofZinc present in an amount Within the range of 5.58.5% by Weight,magnesium present in an amount within the range of 0.550.95% by Weight,chromium present in an amount within the range of 0.0250.25% by weight,titanium present in an amount up to 0.4% by weight, and boron present inan amount up to 0.002% by weight, and less than 0.75 by weight ofimpurities including a maximum of 0.15% by weight of any of the metalsselected from the group consisting of silicon and iron, the balancebeing aluminum.

7. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 6-8% by weight, magnesiumpresent in an amount within the range of 0.60.8% by weight, chromiumpresent in an amount within the range of 0.050.15% by weight, titaniumpresent in an amount within the range of 0.10.25% by weight, and boronpresent in an amount within the range of 0.00050.001% by Weight, andless than 0.75% by weight of impurities including a maximum of 0.15% byweight of any of the metals selected from the group consisting ofsilicon and iron, the balance being aluminum.

8. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 68% by weight, magnesiumpresent in an amount within the range of 06-08% by weight, chromiumpres- '8 ent in an amount within the range of ODS-0.15% by weight,titanium present in an amount within the range of 0.10.25% by weight,and boron present in an amount within the range of 0.00050.001% byweight, and zirconium present in an amount within the range of 0.05-0.25% by Weight, the remainder being aluminum plus minor amounts ofimpurities.

9. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 6-8% by weight, magnesiumpresent in an amount Within the range of 0.60.8% by weight, chromiumpresent in an amount within the range of 0.050.15% by Weight, titaniumpresent in an amount within the range of 0.10.25% by weight, and boronpresent in an amount within the range of 0.00 05-0.001% by weight, andzirconium present in an amount within the range of 0.05- 0.25% byweight, and less than 0.7 5% by weight of impurities, the balance beingaluminum.

10. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 68% by weight, magnesiumpresent in an amount within the range of 06-08% by weight, chromiumpresent in an amount within the range of ODS-0.15% by weight, titaniumpresent in an amount within the range of 0.1-0.25% by weight, and boronpresent in an amount within the range of 0.'00050.001% by weight, andzirconinum present in anamount within the range of 0.05 0.25% by weight,and less than 0.75 by weight of impurities including a maximum of 0.15%by weight of any of the metals selected from the group consisting ofsilicon and iron, the balance being aluminum.

11. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 55-85% by weight,magnesium present in an amount within the range of USS-0.95% by weight,chromium present in an amount within the range of 0.02S0.25% by weight,titanium present in an amount up to 0.4% by weight, zirconium present inan amount up to 0.35 by weight, and less than 0.75% by weight ofimpurities including a maximum of 0.15% by weight of any of the metalsselected from the group consisting of iron and silicon, the balancebeing aluminum.

12. A self-aging aluminum base casting alloy consisting essentially ofzinc present in an amount within the range of 68% by weight, magnesiumpresent in an amount within the range of 06-08% by weight, chromiumpresent in an amount within the range of 0.050.15% by weight, titaniumpresent in an amount within the range of 0.1-0.25% by weight, zirconiumpresent in an amount within the range of 0. 050.25% by weight, and lessthan 0.75% by weight of impuritim including a maximum of 0.15 by weightof any of the metals selected from the group consisting of iron andsilicon, the balance being aluminum.

References Cited in the file of this patent UNITED STATES PATENTS2,146,330 Comstock Feb. 7, 1939 2,290,017 Bonsack July 14, 1942 FOREIGNPATENTS 627,968 Great Britain Aug. 19, 1949

10. A SELF-AGING ALUMINUM BASE CASTING ALLOY CONSISTING ESSENTIALLY OF ZINC PRESENT IN AN AMOUNT WITHIN THE RANGE OF 6-8% BY WEIGHT, MAGNESIUM PRESENT IN AN AMOUNT WITHIN THE RANGE OF 0.6-0.8% BY WEIGHT, CHROMIUM PRESENT IN AN AMOUNT WITHIN THE RANGE OF 0.5-0.15% BY WEIGHT, TITANIUM PRESENT IN AN AMOUNT WITHIN THE RANGE OF 0.1-0.25% BY WEIGHT, AND BORON PRESENT IN AN AMOUNT WITHIN THE RANGE OF 0.0005-0.001% BY WEIGHT, AND ZIRCONINUM PRESENT IN AN AMOUNT WITHIN THE RANGE OF 0.050.25% BY WEIGHT, AND LESS THAN 0.75% BY WEIGHT OF IMPURITIES INCLUDING A MAXIMUM OF 0.15% BY WEIGHT OF ANY OF THE METALS SELECTED FROM THE GROUP CONSISTING OF SILICON AND IRON, THE BALANCE BEING ALUMINUM. 